Microemulsions are thermodynamically-stable, optically-clear emulsions having submicron-sized droplets suspended in a continuous phase. These emulsions form spontaneously, and typically consist of an aqueous phase, an organic phase, and a surfactant/co-surfactant component.
Previous data suggest that volatile lower alcohols, such as ethanol, are required to maintain stable oil-in-water microemulsions. However, topical application of volatile lower alcohols has a drying effect on the skin. Additionally, volatile lower alcohols and compositions containing them are extremely flammable. For these reasons, volatile lower alcohol-containing microemulsions for topical application have seen limited commercial use.
Developing a formulation for a water-immiscible drug that displays desirable drug delivery and solubilization characteristics while meeting other formulation criteria, such as targeted drug concentration, drug stability, bioavailability, safety, and others, is challenging. Currently, many drug delivery systems are available, including liposomes, polymeric/surfactant aggregates, microemulsions. However, these systems have numerous shortcomings, such as low efficiency (e.g., low bioavailability of drug), heterogeneity, and instability of the delivery systems themselves.
There exists a need for a drug delivery vehicle for topical administration wherein a water-immiscible drug may be encapsulated or solubilized.